What size VHF antenna do I need for my boat and radio?
I'm fitting a fixed 25 W VHF and need to choose an antenna. Is a short stainless whip enough, or should I buy a longer fibreglass aerial, and does the radio need a particular size?
Answer
For most sailing yachts, choose a roughly 1 m masthead marine VHF antenna with a nominal 3 dB gain; for most motorboats, start with a 2.4 m fibreglass antenna rated around 6 dB. Your fixed 25 W radio does not need a particular antenna length: correct frequency coverage, mounting height, suitable gain and sound coaxial cable determine its performance.
Check the mounting position
Find a position where the antenna can stand upright, clear of surrounding metal, then measure the cable run to the radio. Marine VHF works mainly by line of sight. Raising a suitable antenna usually achieves more than fitting a longer one in a poor position.
Choose an antenna designed for marine VHF voice frequencies, approximately 156 to 162 MHz, with a 50-ohm connection and a power rating suitable for your transmitter. A normal fixed marine set transmits at up to 25 W; antenna length does not need to match that wattage.
Many fixed radios accept a PL-259 cable plug, but check the radio socket and antenna termination before ordering. Handheld radios often use different connectors. Only connect an external antenna through a manufacturer-approved connection.
Match length and gain
Use these as starting points, rather than strict limits based on hull length:
- Sailing yacht: a roughly 0.9 to 1.2 m stainless whip or compact fibreglass antenna, commonly advertised as 3 dB, mounted at the masthead. Its broader vertical radiation pattern tolerates heel better than a high-gain antenna.
- Small open motorboat or RIB: a roughly 1 to 1.5 m antenna with modest gain, fitted as high as a secure bracket or arch allows. A shorter aerial is often more practical with heavy pitching, limited support or low overhead clearance.
- Cabin motorboat: a 2.4 m, nominal 6 dB fibreglass antenna on the cabin roof or radar arch is a common choice. Fit the mount and any additional support specified by the antenna maker.
- Larger, steady motorboat: a longer, higher-gain antenna can help if the mounting position and support suit the installation. It is rarely the first upgrade for a small boat.
Higher gain concentrates the signal into a flatter pattern; it does not increase transmitter power. This can improve communication near the horizon while the antenna is upright. Heel or pitching can tilt the strongest part of the signal away from the receiving station. Manufacturers do not always quote gain against the same reference, so compare their specifications carefully.